Travelling Call or Not???

[Norm]

Hi Im new to this forum , but I love what I see, I used to play ball and coached a bit and just want more knowledge overall.... So here is a Huge question.

In the pas several years I have seen a growing number of players drive to the basket, pick up thier dribble and take a hop step, (jumping of the ground and landing back down with both feet)how is this legal, and why isnt it an up and down travelling call?
Clearly if u stop dribbling and just straight up and down its a travel, why not in this case?

U always see this in College and now NBA.
Thanks.